Either something has failed in the power supply or something has failed in the NUC's hardware. Compatible power supplies are available from places like Amazon. I suggest you spend the money to get one (or borrow one) and see if this fixes the problem. If it does not, then we will need to look deeper - but we cannot do so until we know that power is clean.
Hope this helps,
You've tried powering on with jumper moved from pins 1-2 to pins 2-3?
You've disconnected power completely and then disconnected the CR2032 battery for 15 minutes?
You've tried performing BIOS Recovery (i.e. placed file GK0066.BIO into root folder of FAT32-formatted USB flash drive, plugged it into system, removed BIOS jumper and then powered on)?
Remove/disconnect any drives, USB devices (including keyboard and mouse), etc. that you have connected to the unit (only thing installed should be memory and only thing connected should be monitor).
If still powers back off, disconnect monitor and try again.
If still powers back off, remove SODIMMs and try again.
If still powers back off, throw in trash.
Thanks for help. I was hopping that Intel will answer as the same topic was few years ago, and only comment that Intel contacted directly via PM for the answer. As I see Intel is not supporting that pc anymore. As I understood that I cannot ask them anymore.
Well, a few years ago, when a NUC failed like this, it would have been replaced under warranty (I will presume that that PM was to ask for personal information (address, etc.) to start the RMA process). Now, though, we're out six years from this NUC's release - and double the warranty period - so that path is unavailable. I hate to see units fail like this, even if they are 6 years old, but it does happen...